theory of calculating the percentage of iron in iron tablets?

Question

theory of calculating the percentage of iron in iron tablets

Answer 1

Measure the mass of one tablet.
Chemically remove the iron but recover the rest of the tablet.
Measure the mass of remainder of the tablet.
Subtract two masses to get amount of iron removed.
Divide amount of iron removed by mass of entire tablet.

Answer 2

Take the mass of the compound
Determine the mass of the iron in the compound.

The key is that there are different iron compounds, and you want the iron, not everything else.

Ferrous sulfate (heptahydrate)
FeSO4·7H2O

Ferrous gluconate

Ferrous fumarate (also known as carbonyl iron)